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When I have a device that is powered by two batteries, can I disable it by turning one battery around?

For illustration, the purpose is to leave batteries in the device for storage, but it does not have an off switch. There are multiple solutions for this, but I would like to understand specifically the solution using reversed batteries.

My idea is as follows: By turning around one of two 1.5 V cells, I let the + poles touch in the middle. The voltage between the - poles should now be 1.5 V - 1.5 V = 0 V. Therefore, there is no current through the device.

The problem is: Two batteries may not be perfectly balanced. One of them may be more discharged than the other, so they have different voltages.

It could work if the battery with more charge would be automatically discharged until it reaches the same level. Then, the cells would get into perfect balance, and stay that way even with fluctuations.

Does that make sense? What properties of the device are required?

If it works with two batteries, does it work too with other even numbers of battery cells?

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    \$\begingroup\$ Assuming these are non-rechargeable alkaline cells, I think you should just try it, then report back with the answer to your own question. It might work satisfactorily enough. \$\endgroup\$
    – user57037
    Commented Sep 9, 2019 at 23:03
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    \$\begingroup\$ it's usually easier tro use a piece of paper, card, or plastic as an insulating shim to break the circuit (just put the paper over the end of one of the battieries), when not in use it can probably be stored besidfe the battery \$\endgroup\$
    – Jasen Слава Україні
    Commented Sep 10, 2019 at 2:32
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    \$\begingroup\$ If you can just disconnect the battery to flip it, why bother turning it around at all? \$\endgroup\$
    – Bort
    Commented Sep 10, 2019 at 14:53
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    \$\begingroup\$ You are assuming the device just uses the two batteries in series. I've seen devices that don't work this way at all. For example, the remote for my cable box uses one battery to power its processor and IR transmitter and uses the other battery to produce a higher voltage just for its RF circuitry. (And yes, when it goes dead, swapping the batteries usually buys me another month or two.) \$\endgroup\$
    – David Schwartz
    Commented Sep 10, 2019 at 16:43
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    \$\begingroup\$ To properly prepare an electronic device for long-term storage 1) take the batteries out of the device, 2) put the device into a plastic bag, 3) evacuate the air from the bag, and 4) seal it securely, 5) put the bag with the device inside it in a cool, dry place away from direct or indirect sunlight, 5) put the batteries in a separate plastic bag, 6) evacuate the air from the battery bag, 7) seal the battery bag securely, and 8) put that bag in the trash or the recycling bin, if you have one. 9) The next time you want to use the device remove it from its bag and install fresh batteries. \$\endgroup\$
    – Bob Jarvis - Слава Україні
    Commented Sep 11, 2019 at 21:55

6 Answers 6

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If the batteries are not perfectly balanced they would still have some net voltage. And that is assuming that the batteries are connected in series.

If the batteries are connected in parallel, flipping one of them the other way around will basically create a dead short between them. At best, that is going to drain them.

In either case, storing batteries in a device is not a great idea. If the device ends up being stored for a longer period than you anticipated, and the batteries start leaking, the internals of the device is hardly an ideal place for them to spill their fluids.

Retrofitting an off switch would be better, although that still doesn't solve the issue of long time storage and leaking.

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    \$\begingroup\$ Yes, they would have a net voltage. But what happens because of that? The difference could get smaller by discharging one cell, until perfect balance. \$\endgroup\$
    – Volker Siegel
    Commented Sep 9, 2019 at 22:24
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    \$\begingroup\$ @VolkerSiegel - No guarantee that they will balance after time. \$\endgroup\$
    – Mattman944
    Commented Sep 9, 2019 at 22:57
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    \$\begingroup\$ Cells in series but reversed. So if current flowing is not zero, then one cell is charging and the other is discharging. So they WILL eventually balance. It is not good to charge alkaline cells, but in practice, if the voltages are very close, I do not think much charge current will flow. I think it will be OK as long as they are not far apart in voltage. \$\endgroup\$
    – user57037
    Commented Sep 9, 2019 at 23:05
  • \$\begingroup\$ @mkeith That's the answer! It means that it will automatically stabilize to 0 V! Feel free to make it a short answer. The others contain lots of useful information that would apply if it were an X-Y-answer. \$\endgroup\$
    – Volker Siegel
    Commented Sep 10, 2019 at 0:18
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    \$\begingroup\$ @VolkerSiegel Even if they zero out eventually, it doesn't remove the risk of a negative voltage in the beginning \$\endgroup\$
    – Mars
    Commented Sep 10, 2019 at 7:25
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You can, but as per @Dampmaskin's answer, it's not really the best plan.

Why not do as often seen in new electronic devices, and inserst a plastic slip between a battery and one of the terminals (or between two batteries). If the slip is long enough to be seen outside the closed battery box, and a clearly visible sign says something like "remove before use", you can just pull the slip to "reactivate" the device.

You can also use posterboard or any other relatively rigid but thin non-conductive material to accomplish the same effect.

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    \$\begingroup\$ You can really use anything non-conductive here. A thick piece of paperboard will also work, and is easy to cut into the appropriate shape. I've used plastic poker chips in devices that take D-size batteries. \$\endgroup\$
    – bta
    Commented Sep 10, 2019 at 19:06
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    \$\begingroup\$ What you say is correct, but not answering the original question at all. \$\endgroup\$
    – Rev
    Commented Sep 11, 2019 at 11:07
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    \$\begingroup\$ @Rev1.0 The help center suggests that answering with a different solution from the one asked is OK: "... Make sure your answer provides that – or a viable alternative. The answer can be “don’t do that”, but it should also include “try this instead”. Any answer that gets the asker going in the right direction is helpful, but do try ..."; This answer offers a different but definitely valid solution to the OPs underlying problem, so I feel this answer is perfectly acceptable and even helpful. \$\endgroup\$
    – marcelm
    Commented Sep 11, 2019 at 15:07
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    \$\begingroup\$ Indeed, people often ask an "X" question when they should be asking what's the best way to achieve "Y". If I see such an XY situation on SE, I don't hesitate to call it out and address the Y instead of the X. \$\endgroup\$
    – Monty Harder
    Commented Sep 11, 2019 at 16:21
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    \$\begingroup\$ @Rev1.0 Sure; but there are currently 4 other answers addressing to some degree the implications of reversing a battery. This answer provides a viable alternative that the OP (or any other reader) might not have considered, and might or might not prefer. I certainly don't think this answer should be the only answer here, but in the current context it just expands the options of anyone reading this question, and I think that's a good thing! :) \$\endgroup\$
    – marcelm
    Commented Sep 12, 2019 at 10:37
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Very often, multiple batteries are series-connected. And the total voltage is used to power "stuff".
In that case, flipping a battery to turn off current works just fine.
However, the less-usual case of parallel-connected batteries won't allow you to flip one: the resulting failure could be spectacular.

It would be unusual, but possible that the series-connected mid-point between the two batteries is used for some purpose. This could be spotted by a wire emerging from the bridge that joins one battery "+" to the other battery "-". If the bridge is free of wires, you're good to go.
Series-connected batteries, one flipped
Keep in mind that battery-flipping as on-off mechanism involves a lot of battery-handling. Keep your fingers off those battery ends where electrical contact is made, and avoid touching the bridge or other electrical contacts. Finger grease/acids can increase contact resistance.
The other obvious caution is to check which battery is flipped!. You can easily apply reverse voltage to your electronics if you guess wrongly. After a few microseconds, you have likely trashed your device.

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    \$\begingroup\$ Flipping the battery in your photo is safe, because the battery case is designed to prevent electrical contact if the polarity is reversed (note the raised plastic around one end of the bridge). In battery cases without this protection, flipping a battery can cause the other batteries to try to charge the flipped one, with potentially catastrophic results. \$\endgroup\$
    – Mark
    Commented Sep 10, 2019 at 22:20
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You can. It is a bad idea for a few different reasons, besides those already listed.

  1. You can yourself forget what you did. Depending on how important is the device, you may swear a lot. Or worse.

  2. Batteries are geometrically asymmetric. Reversing one or more of them will change the length of the battery pack and/or face battery terminal to the wrong contact. You may have hard time inserting them in the battery compartment and/or deform the contacts, the compartment, the cap or something else.

  3. Residual voltage - some (electronic) devices are especially vulnerable to very low voltages and may break in an unexpected manner.

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  • \$\begingroup\$ I love the beginning: "You can. It is a bad idea...". Often people write "Don't do it" or "No, because it would create risk1, risk2,..." or "It would fail because..." instead. These are unclear. \$\endgroup\$
    – Volker Siegel
    Commented Sep 11, 2019 at 9:52
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As others have said, reversing one half of the batteries is likely to work... with some possibilities for trouble (leakage when the batteries expire and so on).

However that only works if your batteries are AAA, AA, C, D or similar cylindrical batteries with end connections... and only under circumstances where the container has open contacts. I've seen battery holders where polarity is 'enforced'... where the +ve end fits against an insulating plate with a hole or slot in it so when you turn the battery round no contact is made at the +ve connector (obviously the -ve end of the battery that is the wrong way round is sitting againstthe +ve end of the holder). The big -ve end of the battery won't fit into the hole or slot so the battery sits against the plastic insulator. That's obviously better than reversing because it's now an open circuit so it doesn't matter if the batteries don't have the same voltage... and you can break the circuit by turning only one battery round in a device with more than two batteries.

If your device uses button batteries, these are often connected to one end and to the side (or sides)... so turning round such a battery means you've got continuous metal between the +ve and -ve connectors of the holder... so the 'other' battery won't see the opposing voltage and the device will receive 1/2 of it's expected voltage. And one battery will run flat.

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As others have said, reversing half of the batteries is likely to work.... for a while. But it depends on what kind of batteries you have. For example, Energizer batteries are guaranteed NOT to leak, whereas Duracell batteries are guaranteed to leak corrosive fluid into your device. If you use Duracells, remove them when your device is in storage.

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